In the related art, laser scanning microscopes used for performing transmission observation and vertical-illumination observation are known (for example, see Patent Literature 1). In order to prevent light other than fluorescence from a sample, such as light from a fluorescent lamp, from entering a photodetector from above the sample in a laser scanning microscope used for performing transmission observation and vertical-illumination observation, the laser scanning microscope is set inside a darkroom or the entire laser scanning microscope is covered with a dark box so as to be used in a dark observation environment.